Chemico-Biological Interactions 186 (2010) 9–15 Contents lists available at ScienceDirect Chemico-Biological Interactions journal homepage: www.elsevier.com/locate/chembioint Gender-related differences in circadian rhythm of rat plasma acetyl- and butyrylcholinesterase: Effects of sex hormone withdrawal  Gracielle Alves-Amaral, Marcelo Pires-Oliveira, Ana Luiza Andrade-Lopes, Tiago Chiavegatti, Rosely Oliveira Godinho ∗ Department of Pharmacology (INFAR), Universidade Federal de São Paulo, 04044-020 São Paulo, SP, Brazil article info Article history: Received 12 January 2010 Received in revised form 14 March 2010 Accepted 2 April 2010 Available online 5 May 2010 Keywords: AChE, acetylcholinesterase AP-1, activator protein-1 ASCh, acetylthiocholine BuChE, butyrylcholinesterase BuSCh, butyrylthiocholine DTNB, 5,5 ′ -dithio-bis(2-nitrobenzoic acid) EDTA, ethylenediaminetetraacetic acid ERE, estrogen responsive element Iso-OMPA, tetraisopropyl pyrophosphoramide Oct-1, octamer-motif-binding factor 1 PEA-3, polyoma enhancer activator 3 Keywords: Acetylcholinesterase Butyrylcholinesterase Sex hormones Circadian cycle Blood abstract The role of acetylcholinesterase (AChE) in the termination of the cholinergic response through acetyl- choline (ACh) hydrolysis and the involvement of plasma butyrylcholinesterase (BuChE), mainly of hepatic origin, in the metabolism of xenobiotics with ester bonds is well known. Besides, BuChE has a crucial role in ACh hydrolysis, especially when selective anticholinesterases inhibit AChE. Herein, we analyzed the gender-related differences and the circadian changes of rat plasma cholinesterases. Plasma and liver cholinesterase activities were evaluated in control or 2–30-day castrated adult male and female rats. Plasma and liver AChE activities did not differ between genders and were not influenced by sex hormone deprivation. BuChE plasma activity was 7 times greater in female, reflecting gender differences in liver enzyme expression. Castration increased liver and plasma BuChE activity in male, while reduced it in female, abolishing gender differences in enzyme activity. Interestingly, female AChE and BuChE plasma activities varied throughout the day, reaching values 27% and 42% lower, respectively, between 2 p.m. and 6 p.m. when compared to the morning peaks at 8 a.m. Castration attenuated daily female BuChE oscil- lation. On the other hand, male plasma enzymes remained constant throughout the day. In summary, our results show that liver and plasma BuChE, but not AChE, expression is influenced by sex hormones, leading to high levels of blood BuChE in females. The fluctuation of female plasma BuChE during the day should be taken into account to adjust the bioavailability and the therapeutic effects of cholinesterase inhibitors used in cholinergic-based conditions such Alzheimer’s disease. © 2010 Elsevier Ireland Ltd. All rights reserved. 1. Introduction Acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) are members of the cholinesterase family, which catalyze the hydrolysis of choline esters with different substrate specificities. Although the essential role of AChE in termination of acetylcholine  Financial support: Fundac ¸ ão de Amparo à Pesquisa do Estado de São Paulo (FAPESP); R.O.G project grant 05/59006-1, Brazil; Conselho Nacional de Desenvolvi- mento Científico e Tecnológico (CNPq), Brazil; Conselho de Aperfeic ¸ oamento de Pessoal de Ensino Superior (CAPES), Brazil. ∗ Corresponding author at: Department of Pharmacology, Universidade Federal de São Paulo, Rua Três de Maio, 100, 3rd floor, 04044-020 São Paulo, SP, Brazil. Tel.: +55 11 55764447; fax: +55 11 50813849. E-mail address: godinho@unifesp.br (R.O. Godinho). signaling at central and peripheral synapses is well recognized, the physiological significance of high amounts of AChE and BuChE that are found in plasma [1] remains unclear. Blood BuChE catalyses the hydrolysis of a wide variety of choline and non-choline esters and toxins [2], and it is clinically important because it metabolizes the short-acting muscle relaxant succinyl- choline as well as ester-type local anesthetics and cocaine [3–6]. Some patients have an ‘atypical’ variant of BuChE with reduced catalytic activity, which explains prolonged apnea after adminis- tration of usual therapeutic doses of succinylcholine [3]. However, the relevance of BuChE has gained a new dimension because of its ability to hydrolyze ACh. Indeed, BuChE activity is responsible for the survival of AChE knockout mice that lack AChE activity [7], demonstrating that BuChE can totally replace AChE in ACh hydrol- ysis. In fact, past as well as recent studies suggest that AChE and 0009-2797/$ – see front matter © 2010 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.cbi.2010.04.002